The addition of organic substances to acid copper electrolyte bath, including for example, copper sulfate electrolytes, has been well known in the art for depositing bright copper layers instead of a crystalline matte deposit. These additives include, for example, polyethylene glycol, thiourea and derivatives thereof, thiohydantoin, thiocarbaminic acid ester and thiophosphoric acid ester, safraninines, thiourea-formaldehyde condensates and certain C═S compounds. The foregoing additives have traditionally been used as additives for acid copper electrolytes, including copper sulfate electrolytes, to obtain bright copper coatings. In addition, polymeric phenazonium compounds have also been developed for use in acid copper electrolytes for depositing bright, level copper coatings and can be used alone or in combination with these other organic substances.
As described for example in U.S. Pat. No. 3,743,584 to Todt et al., the subject matter of which is herein incorporated by reference in its entirety, a polymeric phenazonium compound may be prepared by diazotizing an amino solution in an acid solution and subsequently boiling down of the resulting diazonium salt.
The diazotization of the amino compound is typically accomplished by suspending the monomer in a solution of a strong acid, such as sulfuric acid, hydrochloric acid, acetic acid, fluoroboric acid, phosphoric acid and/or another suitable acid. The acids form the diazonium acid radical. Boiling down of the formed diazonium salt takes place at a temperature that is typically within the range of about 5 to 100° C., preferably about 10 to 25° C. The reaction products precipitate from the acid reaction solution or can be precipitated therefrom by neutralization with a base such as ammonia or a hydroxide, such as potassium hydroxide.
Polymeric phenazonium compounds prepared in accordance with this process typically have the general formula:
wherein R1, R2, R4, R5, R6, R8 and R9 are the same or different, and represent hydrogen, a low alkyl or a substituted aryl, R3 starts with NH2 and is diazotized followed by polymerization, R5 and R8 may alternatively represent monomeric or polymeric phenazonium radicals, R7 with its substituent group is a substituted amine with, RX and RY representing any combination of CH3, C2H5 
and hydrogen, except that RX and RY cannot both be hydrogen, A is an acid radical, and n is an integer from 2 to 100.
As lower alkyl radicals, methyl, ethyl, and propyl may be used among others.
As aryl radicals, phenyl, which may be substituted by methyl, ethyl, methoxy, ethoxy, etc., among others may be used.
Examples of polymeric phenazonium compounds of this type include poly(6-methyl-7-dimethylamino-5-phenyl phenazonium sulfate); poly(2-methyl-7-diethylamino-5-phenyl phenazonium chloride); poly(2-methyl-7-dimethylamino-5-phenyl phenazonium sulfate); poly(5-methyl-7-dimethylamino phenazonium acetate); poly(2-methyl-7-anilino-5-phenyl phenazonium sulfate); poly(2-methyl-7-dimethylamino phenazonium sulfate); poly(7-methylamino-5-phenyl phenazonium acetate); poly(7-ethylamino-2,5-diphenyl phenazonium chloride); poly(2,8-dimethyl-7-diethylamino-5-p-tolyl-phenazonium chloride); poly(2,5,8-triphenyl-7-dimethylamino phenazonium sulfate); and poly(7-dimethylamino-5-phenyl phenazonium chloride), by way of example and not limitation.
While these polymeric phenazonium compounds continue to enjoy success as additives for copper electroplating baths, it is would be desirable to provide a process of making these polymeric phenazonium compounds that requires fewer steps and that produces an additive having a smaller quantity of unreacted monomer remaining in the end product than the production methods of the prior art.